When you have to do etests ? do they send you a letter or something ? I never done one

Depending on vehicle age. If a vehicle is new its something like every 5 years and as it gets older its every 2 years. After 20 years its basically free for all and up to police to pull you off if your significantly puffing.

I know Budds does it now.
SInce Jan of this year Ministry forced guys that do emissions to buy new system that does not use dyno anymore. They plug into your OBD2 system and here ' e go. I have heard of some problems with the system, since if you have had any issues with trouble codes, and got erased just before the test.... well, the computer still remembers the trouble and even though you don't have any codes showing now, you may fail just because your car did not clear all the faults out of the system yet. After you clear it you will need about 20 KMs before the computer will assume that there is no more codes present.
So if you ever thought that by clearing the codes just before the test is going to help you. welll.... it is not going to happen ( now )
If you have the check engine light on, it is automatic FAIL, retest is 50% off the initial cost.
This is all I know about this new system.
I'm sure that some of us will chime in with more and more info about this new way of testing our cars...

I've never had a check engine light in my car, except for when the eccentric shaft sensor had to be changed. However, I occasionally have the passenger airbag light come on, since that mat sensor is faulty. I'm assuming these tests ignore codes unrelated to emissions, though.